Manufacturing a papery article

ABSTRACT

The present invention relates to a process for manufacturing papery articles, such as paper, card and board, comprising the pH adjustment of an aqueous composition comprising at least one fiber stock by addition of methanesulfonic acid (MSA).

The present invention relates to a process for manufacturing paperyarticles, such as paper, card and board, comprising the addition ofmethanesulfonic acid (MSA) to an aqueous composition comprising at leastone fiber stock to set the pH.

The present invention further relates to the use of methanesulfonic acidin the manufacture of a papery article, more particularly for settingthe pH of an aqueous composition comprising at least one fiber stock inthe paper/board machine approach flow.

Paper and papery article for the purposes of the present invention referto sheetlike articles manufactured from fibers, more particularly fromchemically or mechanically uncovered vegetable fibers, which are formedby dewatering a fiber stock suspension using at least one wire screenusually under addition of fillers and further additives.

The manufacture of papery articles on state of the art paper/boardmachines generally comprises the dewatering of a fiber stock suspension,for example a chemical pulp, mechanical pulp and/or waste papersuspension, on at least one moving wire screen to form a paper web. Theterm paper or board machine typically subsumes the following assemblies:approach flow system, head box, wire section, press section, dry end,size press (surface sizing), film press, smoothing cylinder, smoothingsystem, online calender, online coating assembly and windup. Often, themanufacture of papery articles comprises downstream steps of surfacetreatment (e.g., calendering, coating) and comprises finishing (e.g.,roll cutting, format cutting, packing). A general description of theprocess steps and equipment parts involved in the manufacture of paperyarticles is described for example in “Papiermacher Taschenbuch, 8^(th)edition, Dr. Curt Haefner-Verlag GmbH, Heidelberg”.

The approach flow system is where the fiber stock suspension is mademachine-ready for the subsequent sheet forming in the wire section. Itis where, for example, the final/compensatory beating of the fiber stockis carried out, the stock amounts and stock densities are regulated, andalso the regulation of the flow rates is carried out. Within theapproach flow system, it is also possible for the metered addition offillers, process chemicals and/or performance chemicals to take place.The approach flow system is generally held to include all equipmentparts and pipework between the mixing and machine chest and the head boxof the paper/board machine. The approach flow system of the paper/boardmachine is generally also where the pH of the fiber stock suspension isset.

In the head box, the fiber suspension having a stock density ofgenerally less than 1.4% is applied to at least one moving endless wirescreen (machine wire). In the subsequent wire section as it is known,the fiber stock suspension is drained to a stock density of about 12 to24% (augmented by application of vacuum or pressure for example) and thefibers become interfelted together to form a still wet fibrous web(sheet formation). This fibrous web is removed from the wire using apickup felt (felt band) for example, and passes into the subsequent wetpresses where the stock density is further increased to about 50%.

Thereafter, the fibrous web is generally dried in the dryer sectionusing drying cylinders. For certain end uses, the paper can then besubjected to further processing steps (e.g., smoothing, coating,calendering).

The fiber stock suspensions used for paper or board manufacture, inaddition to fibers, usually comprise fillers, more particularlyinorganic fillers such as calcium carbonate, kaolin, titanium dioxide,barium sulfate and multiple process and/or performance chemicals, forexample sizing agents to increase the hydrophilicity and printability ofthe paper, and also, for example, retention aids, drainage aids, dyes,optical brighteners, wet strength agents, dry strength enhancers,defoamers, biocide.

Possible fiber stocks for the manufacture of papery articles aregenerally primary fiber stocks and also secondary fiber stocks. Primaryfiber stocks used are more particularly wood-free fiber stocks, moreparticularly chemical pulps such as sulfate pulp (SA) (also known askraft pulp), sulfate semi-pulp, sulfite pulp (SI) of hard- and/orsoftwoods. However, wood-containing fiber stocks, more particularlymechanical pulps such as groundwood (HS) (also known as stone groundwoodSGW), pressurized groundwood (PGW), refiner mechanical pulp (RMP),thermomechanical pulp (TMP), chemical thermal mechanical pulp (CTMP) andthermomechanical pulp with caustic-peroxide pretreatment (BCTMP) mayalso be used. Secondary fiber stocks include various waste papervarieties recycled into paper/board and card production, and alsodeinked pulp (DIP). DIP is produced by a waste paper recovery process inwhich a large proportion of the printing ink is removed from the fiberstock suspension. In the deinking process, the slurried, defibered wastepaper is commonly admixed with caustic, water glass, complexing agent,surfactant and hydrogen peroxide. The printing inks detach from thefiber surface and are removed from the fiber stock suspension byflotation. Chemical pulp, such as goundwood, pressurized groundwood,TMP, RMP, but also chemical pulp are typically bleached in the course ofproduction and/or before use. A distinction is generally made betweenoxidative and reductive bleaching stages, although these bleachingstages are often combined into bleaching sequences. Bleaching frequentlycomprises a treatment with hydrogen peroxide under alkaline conditions.When the bleaching process concludes with an alkaline stage, it isgenerally necessary for the fiber stock suspension to be acidified. Inorder to establish the pH necessary for paper production, it istherefore generally necessary to add an acid to regulate the pH.

Depending on the pH of the fiber stock suspension used for paperformation, a general distinction is made between the conventional acidicprocess (pH in the range from 4.5 to 6.8) comprising generally theaddition of acidic aluminum salts and the neutral process in the pHrange from 6.8 to 10.8. In the ideal case of a neutral process, the pHis adjusted to a value between 7.0 to 7.5. In recent decades, theneutral process has become more and more established, particularlybecause it enables calcium carbonate (CaCO₃) to be used as a filler, forexample in the form of ground calcium carbonate (GCC) or precipitatedcalcium carbonate (PCC).

Fiber stock suspension pH is of decisive importance for paper productionand has a direct influence on paper/board machine runnability. A high pHleads to increased swelling of the fibers and impedes fiber stocksuspension drainage. Accurate and reliable pH setting furthercontributes to preserving the whiteness of the papery articles and topreventing yellowing by alkalis. The choice of suitable acids forsetting the pH as part of the manufacture of papery articles is verylimited. Owing to the requirements of availability, price and stability,a person skilled in the art chooses from a very limited number of acidssuitable for paper production. The use of phosphoric acid, or of acombination of phosphoric acid and phosphonates, or the use of carbondioxide for pH setting is described in the prior art. It is furtherknown to use sulfuric acid and/or bisulfite to set the pH in paperproduction. It has also been written that the pH of a fiber stocksuspension can be adjusted by adding an electrolyte, such as aluminumsulfate, aluminum nitrate, polyaluminum chloride (PAC) and aluminumhydroxide chloride.

The WO 98/56988 document describes a process for stabilizing the pH of apulp suspension for paper production using a combination of an alkalimetal hydroxide and carbon dioxide.

The US 2010/0175839 document describes a multi-stage process foradjusting the pH of a cellulosic pulp suspension wherein the pulp istreated at least twice with carbon dioxide and at least once with astrong acid, e.g., sulfuric acid, sulfurous acid or bisulfite, andwherein a step for carbonate removal is included.

The WO 2009/003770 document discloses a process for making paper whereina fiber stock suspension comprising a mechanical pulp is subjected to anacid-base treatment to avoid reducing the brightness. In the process,the fiber stock suspension is treated initially with a strong acid, moreparticularly sulfuric acid, sulfurous acid, hydrochloric acid andbisulfite, and then with a weak base (e.g., an alkali metal bicarbonateor alkali metal carbonate).

The prior art use of phosphoric acid and phosphonates results inincreased formation and deposition of calcium phosphates in variousparts of the paper machine. The paper/board machine thus has to beincreasingly idled to allow for cleaning.

Many state of the art paper machines operate at very high speeds of upto 1800 meters per minute and outputs of up to 1000 t of paper per 24 hto increase the production of paper/card. Paper/board machine idling andthe increased production of broke are therefore the decisive factors forthe efficiency and economics of the production process.

Furthermore, phosphorus compounds pollute the wastewater cleaningfacilities of paper mills which, unlike communal water treatmentfacilities, generally have no phosphorus-eliminating stage.

One particular problem with using carbon dioxide for pH regulation offiber stock suspensions is the outgassing of carbon dioxide in the wirewater circuit and also the attendant fluctuations in the pH. Inaddition, metering the gaseous additive carbon dioxide requires costliermetering devices.

It is an object of the present invention to provide a pH-regulatingadditive, more particularly an acid, for fiber stock suspensions inpaper production, and/or an improved process for paper production. Theprocess should firstly meet all wastewater-relevant and environmentalrequirements as well as provide for an efficient, simple and inexpensiveoperation. Simple metering, minimal introduction of additional saltcontent into the wire water/wastewater of the paper machine and alsogood drainage behavior of the fiber stock suspension should be ensuredfor instance.

We have found that, surprisingly, adding methanesulfonic acid (MSA) is aparticularly effective way to adjust the pH of fiber stock suspensionsin papermaking. Methanesulfonic acid has a pK_(a) value of about −0.6and so is a strong or very strong acid. Methanesulfonic acid isgenerally non-oxidizing and is marked by heat and hydrolysis resistancein particular. Methanesulfonates are used in washing and cleaningcompositions for example. Methanesulfonic acid is further used in acidicelectroplating solutions for metal coatings.

The present application is directed to a process for manufacturing apapery article, such as paper, card and board, comprising the steps of:

-   -   a) providing an aqueous composition comprising at least one        fiber stock;    -   b) adding methanesulfonic acid to the aqueous composition        comprising at least one fiber stock to adjust the pH;    -   c) draining the aqueous composition comprising at least one        fiber stock.

The use of methanesulfonic acid is associated with the followingadvantages in particular:

-   -   Methanesulfonic acid is readily biodegradable and is        halogen-free and thus reduces the burden on the wastewater        treatment of the production process. Moreover, no or distinctly        less phosphorus/phosphate ends up in the wastewater of the        paper/board machine.    -   There is less, if any, formation of deposits of calcium        phosphate, for example, in the parts of the paper/board machine.    -   Owing to the high acid constant of methanesulfonic acid,        comparatively low quantities need to be added. The salt burden        of process waters in papermaking can accordingly be reduced.    -   Economic viability/efficiency of the manufacturing process is        improved.    -   Methanesulfonic acid is colorless, odorless and available in        high purity, hence there is no alien impact on the manufacturing        system (process water, wastewater, circuit water, papery        articles). Therefore, methanesulfonic acid is particularly        suitable for use in the manufacture of papery articles        (packaging materials for example) which are used in the food        sector.    -   Methanesulfonic acid has high thermal stability, a low vapor        pressure, hydrolysis resistance and unlimited miscibility with        water, hence handling and metering are simple.    -   Methanesulfonic acid is halogen-free and has minimal corrosivity        compared with sulfuric acid for example.

The use of methanesulfonic acid is thus able to provide a distinctimprovement in the economics of manufacturing papery articles.

Paper and papery article for the purposes of the present invention referto sheetlike articles manufactured from fibers, more particularly fromchemically or mechanically uncovered vegetable fibers, which are formedby dewatering a fiber stock suspension using at least one wire screenusually under addition of fillers and further additives. Additives aregenerally distinguished into process chemicals (e.g., biocides,deaerators, retention aids) and performance chemicals (e.g., dyes,optical brighteners, wet strength agents). Paper and papery articles forthe purposes of the present invention are more particularly graphicpapers, office communications papers, packaging papers, hygiene papersand specialty papers. Graphic papers for the purposes of the inventionare all papers used for printing in flexographic printing, letterpress,offset printing or gravure printing for example, e.g., news print.Office communication papers are writing, printing and copying papers,for example photoprint and digital printing papers. Packaging papers arepapers, card and board for packaging purposes, for example corrugatedfiberboard. Hygiene papers for the purposes of the invention are papersof high specific volume and high absorbency, which are typically used inthe sanitary or kitchen sector or in the industrial sector. The termspecialty papers identifies papers and paperboards for specifictechnical uses, for example decor papers and filter papers.

Papery articles can be classified, according to their mass per unitarea, as paper, card or board. According to German standardspecification DIN 6730, a mass per unit area of not more than 225 g/m²is indicative of paper and above 225 g/m² of board. Papery articleshaving a mass per unit area in the range from 7 to 150 g/m² are oftenalso referred to as paper, in the range from 150 to 600 g/m² ascardboard and from 600 g/m² as paperboard. Cardboard and paperboardtypically consist of multiple layers.

The present invention more particularly provides a process as describedabove, wherein the step of draining the aqueous composition (step c)results in the formation of a fibrous web which is pressed and/or driedin one or more further process steps.

The aqueous composition more particularly is a suspension (slurry) of afiber stock in water. The aqueous composition may comprise furtherdissolved, colloidally dissolved or solid constituents. The constituentsin question are more particularly known to a person skilled in the artand used/generated in the course of manufacturing papery articles.

The fiber stock can be more particularly selected from:

-   -   chemical pulp (ZS), such as sulfate pulp (SA) (also called kraft        pulp), sulfate semichemical pulp, sulfite pulp (SI);    -   mechanical pulp, such as groundwood (HS) (also called stone        groundwood SGW), pressurized groundwood (PGW), refiner        mechanical pulp (RMP), thermomechanical pulp (TMP), chemical        thermomechanical pulp (CTMP), thermomechanical pulp with        caustic/peroxide pretreatment (BCTMP);    -   secondary fiber stock, such as waste paper (AP) and deinked pulp        (DIP).

Fiber stocks used can be more particularly the above-described bleachedand/or unbleached pulps and/or fiber stocks from hard- or softwoods.Preference is given to using beech sulfite pulp and/or long fibersulfate pulp.

More particularly, the aqueous composition comprises at least one fiberstock selected from the group consisting of sulfate pulp (SA), sulfatesemi-pulp, sulfite pulp (SI), groundwood (HS), pressurized groundwood(PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP),chemical thermomechanical pulp (CTMP), thermomechanical pulp withcaustic/peroxide pretreatment (BCTMP), waste paper (AP) and deinkedwaste pulp (DIP).

In a preferred embodiment, the fiber stock used is at least onesecondary fiber stock, more particularly waste paper and/or deinked pulp(DIP).

More preferably, the aqueous composition comprises at least one fiberstock which has been alkali-oxidatively bleached.

Preferably, the aqueous composition comprising at least one fiber stockhas a stock density in the range from 0.01 to 5%, preferably in therange from 0.1 to 5% and more preferably in the range from 0.2 to 1.4%.

The stock density of an aqueous composition comprising at least onefiber stock (fiber stock suspension) is the percentage of the dry massof the filterable solids in the composition relative to the mass of theentire composition. Commonly, the dry mass is reported as absolute drymass or as dry mass on drying under standard conditions (oven dry,otro). The determination of the stock density of fiber stock suspensionsis described in DIN 54359 (EN ISO 4119) for example.

By further constituents, the aqueous composition may comprise at leastone customary additive (process and performance chemicals) known to aperson skilled in the art. The additive may be selected from:

-   -   process chemicals, such as        -   electrolyte, for example aluminum sulfate, aluminum nitrate,            polyaluminum chloride (PAC), aluminum hydroxide chloride,            inorganic precipitants        -   organic precipitant        -   biocide (e.g., slime control agent)        -   deaerator        -   defoamer        -   dispersant        -   adsorbent (e.g., talc)        -   fixative (e.g., short-chain cationic polymers)        -   retention aid (e.g., long-chain anionic and cationic            polymers, also partially crosslinked)        -   drainage accelerant    -   and performance chemicals, such as        -   dye        -   optical brightener        -   internal sizing agent (resin size, AKD, ASA, polymer size)        -   surface sizing agent        -   wet strength agent        -   dry strength enhancer        -   internal wet web strength polymer (IWWS)

More particularly, the aqueous composition additionally comprises atleast one further additive selected from the group consisting ofaluminum sulfate, aluminum nitrate, polyaluminum chloride (PAC),aluminum hydroxide chloride, organic precipitant, biocide, deaerator,defoamer, dispersant, adsorbent, fixative, retention aid, drainageaccelerant, dye, optical brightener, internal sizing agent, wet strengthagent, dry strength enhancer and internal wet web strength polymer(IWWS).

Preferably, the aqueous composition additionally comprises at least oneinorganic filler selected from the group consisting of ground calciumcarbonate (GCC), precipitated calcium carbonate (PCC), kaolin, titaniumdioxide and barium sulfate, preferably selected from the groupconsisting of ground calcium carbonate (GCC) and precipitated calciumcarbonate (PCC).

Adjusting the pH of an aqueous composition comprising at least one fiberstock is more particularly effected by adding methanesulfonic acid untilthe desired pH value or the desired pH range is reached. A personskilled in the art is familiar with common methods of pH control. Theamount of methanesulfonic acid added depends on the type of the aqueouscomposition comprising at least one fiber stock and its original pH andalso the desired pH target value.

Adjusting the pH of the aqueous composition comprising at least onefiber stock can be effected by adding a mixture of acids comprisingmethanesulfonic acid. It is further conceivable to use a mixture ofmethanesulfonic acid and carbon dioxide, or a mixture of acidscomprising methanesulfonic acid and carbon dioxide. More particularly,methanesulfonic acid is added as sole acid to adjust and/or stabilizethe pH. It is further conceivable to adjust/regulate the pH of theaqueous composition by additionally adding a base known to a personskilled in the art.

The present invention provides more particularly a process formanufacturing a papery article as described above, wherein the pH of theaqueous composition comprising at least one fiber stock is adjusted to avalue in the range from 4 to 11, more particularly in the range from 4.5to 6.8 and more particularly in the range from 6.8 to 10.8.

When the process of the present invention relates to a process formanufacturing a papery article using the acidic method, it isparticularly a pH in the range from 4.5 to 6.8 which is set by addingmethanesulfonic acid. When the process of the present invention relatesto a process for manufacturing a papery article using the so-calledneutral method (usually with use of calcium carbonate as filler), the pHof the aqueous composition comprising at least one fiber stock ispreferably adjusted to a range from 6.8 to 10.8 and more particularlyfrom 7.0 to 7.5.

The process described in the present application for manufacturing apapery article may comprise further common process steps of paper/boardproduction, for example steps in stock preparation comprisingdispersing, sorting, beating of the fiber stock, steps downstream ofdrying, such as calendering, coating, cutting, and also steps concerningfinishing.

The addition of methanesulfonic acid to the aqueous compositioncomprising at least one fiber stock can take place at one or moredifferent process sections of the manufacturing process of the paperyarticle. More particularly, the addition of methanesulfonic acid to theaqueous composition comprising at least one fiber stock takes place in apaper machine approach flow.

The approach flow system for the purposes of the present invention isgenerally held to include all equipment parts and pipework between themixing and machine chest and the head box of the paper/board machine.The approach flow system is where the fiber stock suspension is mademachine-ready for the subsequent sheet forming in the wire section. Itis where, for example, the final/compensatory beating of the fiber stockis carried out, the stock amounts and stock densities are regulated, andalso the regulation of the flow rates is carried out. The approach flowsystem of the paper/board machine is where more particularly the aqueouscomposition comprising at least one fiber stock (fiber stock suspension)is uniformly diluted from about 3 to 5% stock density (thick stock) toabout 0.2 to 1.4% stock density. In addition, the fiber stock suspensioncan be cleaned of fiber bundles, sand, plastics, etc. This is done moreparticularly in the so-called stock fine screening via centrifugal,pressure and/or vibration screeners for example. The approach flowsystem is also where fillers, process chemicals and/or performancechemicals can be added. The approach flow system of the paper/boardmachine is generally also where the pH of the fiber stock suspension isset.

It is particularly preferable for the addition of methanesulfonic acidfor adjusting the pH to take place before, after and/or during the stockfine screening of the aqueous composition comprising at least one fiberstock. Stock fine screening is more particularly effected using commonscreening assemblies, for example centrifugal, pressure and/or vibrationscreeners. It is preferable to add methanesulfonic acid before the lastscreening assembly before the head box.

The process of the present invention can generally be used formanufacturing any papery articles known to a person skilled in the art.The process of the present invention relates more particularly to themanufacture of a papery article selected from graphic paper, officecommunication paper, packaging paper, card, board, hygiene paper andspecialty paper, preferably a process for manufacturing a graphic paperor an office communication paper. In a preferred embodiment, theinvention provides a process for manufacturing a papery article whereinthe papery article is a packaging material for the food sector.

The present application is further directed to the use ofmethanesulfonic acid in the manufacture of a papery article.

More particularly, the use which the present invention provides formethanesulfonic acid in the manufacture of a papery article comprisesadjusting the pH of an aqueous composition comprising at least one fiberstock.

More particularly, the present invention provides for the use ofmethanesulfonic acid in the manufacture of papery articles onindustrially common paper and/or board machines. Preferably, the use ofmethanesulfonic acid comprises adjusting the pH of an aqueouscomposition comprising at least one fiber stock in a paper and/or boardmachine approach flow. The methanesulfonic acid may be more preferablyused before the head box.

More particularly, the present invention provides for the use ofmethanesulfonic acid in the manufacture of a papery article selectedfrom graphic paper, office communication paper, packaging paper, board,card, hygiene paper and specialty paper, more particularly a packagingmaterial for the food sector.

1-12. (canceled)
 13. A process for manufacturing a papery article comprising the steps of: a) providing an aqueous composition comprising at least one fiber stock; b) adding methanesulfonic acid to the aqueous composition comprising at least one fiber stock to adjust the pH; and c) draining the aqueous composition comprising at least one fiber stock.
 14. The process according to claim 13, wherein the step of draining the aqueous composition (step c) results in the formation of a fibrous web which is pressed and/or dried in one or more further process steps.
 15. The process according to claim 13, wherein the fiber stock used is at least one fiber stock selected from the group consisting of sulfate pulp (SA), sulfate semi-pulp, sulfite pulp (SI), groundwood (HS), pressurized groundwood (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemical thermomechanical pulp (CTMP), thermomechanical pulp with caustic/peroxide pretreatment (BCTMP), waste paper (AP) and deinked waste pulp (DIP).
 16. The process according to claim 13, wherein the aqueous composition comprises at least one fiber stock which has been alkali-oxidatively bleached.
 17. The process according to claim 13, wherein at least one secondary fiber stock is used.
 18. The process according to claim 13, wherein the aqueous composition comprising at least one fiber stock has a stock density in the range from 0.01 to 5%.
 19. The process according to claim 13, wherein the aqueous composition additionally comprises at least one further additive selected from the group consisting of aluminum sulfate, aluminum nitrate, polyaluminum chloride (PAC), aluminum hydroxide chloride, organic precipitant, biocide, deaerator, defoamer, dispersant, adsorbent, fixative, retention aid, drainage accelerant, dye, optical brightener, internal sizing agent, wet strength agent, dry strength enhancer and internal wet web strength polymer (IWWS).
 20. The process according to claim 13, wherein the aqueous composition additionally comprises at least one inorganic filler selected from the group consisting of ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin, titanium dioxide and barium sulfate.
 21. The process according to claim 13, wherein the pH of the aqueous composition comprising at least one fiber stock is adjusted to a value in the range from 4 to
 11. 22. The process according to claim 13, wherein the step of adding methanesulfonic acid to the aqueous composition comprising at least one fiber stock takes place in a paper machine approach flow.
 23. The process according to claim 13, wherein the papery article is selected from graphic paper, office communication paper, packaging paper, board, card, hygiene paper and specialty paper.
 24. The process according to claim 13, wherein the papery article is a packaging material for the food sector. 